The present invention is concerned with the control of reception apparatus and especially in situations where transmission include an identifier identifying the origin of the transmission. For example, a broadcast television transmission may contain a coded identifier which identifies the particular broadcast television service.
According to the present invention, there is provided an apparatus for receiving broadcast transmissions, which transmissions contain identifiers identifying the origin of the transmission, the apparatus including:
a store for storing data identifying transmissions which the apparatus is or is not permitted to receive;
means for loading the store with such data; and
means for comparing received identifiers with the contents of the store and to enable or disable in dependence on the result of the comparison; wherein the apparatus has a fixed part and a removable part, the removable part containing a further store containing the said data and the loading means being operable to transfer the contents of the further store into the first-mentioned store.
xe2x80x9cBroadcastxe2x80x9d in this context may refer to transmissions sent by radio, but the invention could also be applied to other forms of distribution such as optical fibre networks or cables (as used for cable television for example). Each transmission could be on a different frequency; alternatively, a time division multiplex system might be used, with several transmissions (each with its own identifier) carried in a single multiplex signal, or a combination of frequency-division and time-division multiplexing might be employed.
Other aspects of the invention are set out in the sub-claims.